The use of the getter materials in the manufacture of electronic tubes is well known. A commonly used getter assembly consists of a U-shaped channel getter material container in annular form with a getter material contained within the channel. This assembly is mounted within an electron tube, for example, a color television picture tube. After the tube is evacuated, the residual gases left in the tube are reroved by heating the getter assembly and getter material contained therein to a high temperature, suitably by induction heating, whereupon the getter material is flashed or vaporized. The vaporized getter material absorbs or reacts with the residual gases and removes them as low vapor pressure solid condensates and continues to absorb any further liberated gases throughout the life of the tube.
Usually the getter material principally comprises: a mixture or preferably an alloy of metals such as, for example, barium and aluminium. It is the barium component of this alloy which provides the reactive material. The clean up of residual gases in television picture tubes, and particularly color tubes, requires a relatively large amount of active barium material. For example, a 25 inch screen color tube having three electron guns and a metal shadow mask has been found to require a yield of 175 to 225 mg of barium. Since the barium-aluminium alloy might have contained up to about 50 percent aluminium, the total amount of alloy in the container before flashing could be from 350 to 450 mg. It has further been found desirable to employ exothermic gettering powders in color television picture tubes. An exothermic gettering powder can comprise: a barium-aluminium alloy or mixture plus about an equal weight of powdered nickel. The nickel reacts exothermically with the aluminium upon heating to supply additional heat for evaporating the barium. The self-generated heat lessens the getter flasking time from 30 seconds for an endothermic type getter to 15 or 20 seconds witn the exothermic type getter.
A typical channel ring exothenaic getter assembly used in color television picture tubes thus may contain, for example, 1000 mg of a 25 weight percent barium-25 weight percent aluminium-50 weight percent nickel exothermic alloy yielding about 200 mg of barium on heating. The getter container itself may comprise a U-shaped channel formed into a ring of, for example, about 2.54 cm outside diameter and having a channel width of 0.5 cm Alternatively, the outer diameter may be about 1.5 or 2 cm and the channel width may be about 0.5 cm. Tne getter powder is pressed into the channel. The flashing of the getter requires heating to a high temperature, about 1300.degree. C., to vaporize the barum, or whatever getter material is utilized. As a result of this heating the residue and the channel ring container are themselves heated to a high temperature. This heating results in the melting or sintering of the residue, eitner the aluminium powder in an exothermic getter, the barium-nickel-aluminium powder in the case of the exothermic alloy described above, or whatever unflashed material is present. The container itself, generally stainless steel, is itself heated to a temperature often near its melting point, and in the case of improperly formed or positioned getter assemblies, the stainless steel ring may melt.
The presence of the extremely hot getter container in a glass-walled electron tube can cause serious problems as will be seen from the following: an electron tube, particularly a television picture tube generally comprises a neck portion in which are located the electron gun or guns and auxiliary equipment; an enlarged bulb portion which terminates in a generally flat viewing screen; and a funnel-shaped portion joining the neck and bulb portions. Whereas in the past, the ring shaped getter container was usually mounted in the neck portion of the tube positioned on the electron gun, it is now a desired practice to mount the getter container in or near the funnel portion of the tube. Since the getter container must be outside the path of the stream of electrons directed from the electron gun toward the screen and since the diameter of the funnel cross-section at the selected site may be only slightly larger than that of the neck portion, it is necessary to have the getter container actually abutting against the wall of the tube. This is accomplished by mounting the getter container at the end of a spring-like metallic strip support or "antenna", the other end of which is fixed to a wall of the electron gun in tne neck portion of the tube. The spring is biased to force the getter container against the wall of the tube in the funnel portion and thus keep clear the path for the electron beam.
Another widely used getter device mounting position is in the region of the anode button. Usually the getter assembly is attached to a small leaf spring. The leaf spring is then attached by suitable means to the anode button, the resilience of the spring forcing the getter assembly against the wall of the tube.
This positioning of the getter assembly in direct contact with the glass walls of the tube can and often does cause cracking of the glass when the getter assembly is heated inductively to high temperatures during flashing. Since the television tube is for the most part completely fabricated just prior to gettering, the cracking of the tube at this time is a substantial loss. In addition, it is important that the getter assembly be properly aligned inside the tube so that the gettering flash is properly directed. Such alignment is difficult to achieve using normal production line techniques. Even if the getter assembly is distanced from the wall by wire runners, for instance, the high temperatures encountered during flashing can cause the support spring or other metallic parts to soften causing the getter device to change its orientation relative to the induction coil thus provoking all the inconveniences described in U.S. Pat. No. 3,558,961.
Getter assemblies having high barium yields and providing protection against thermal breakage of television picture tubes have been described in U.S. Pat. No. 3,390,758 assigned to Union Carbide Corporation and U.S. Pat. No. 3,381,805 assigned to SAES GETTERS S.p.A. The means of protection against thermal breakage of the television picture tube or kinescope was by means of the provision on the getter device of a ceramic support material having a low thermal conductivity and being opague to thermal radiation.
Unfortunately, these assemblies even when having a central core opening are very heavy and in consequence the spring or "antenna" which is used to hold the getter device in position on the wall of the kinescope has to be heavily biased tensioned. This is to prevent the excessive vibration of the kinescope that occurs, for example, during transport which causes the getter assembly to momentarily detach itself from the kinescope wall and on being constrained to go to its original position causes such a sharp impact as to damage the kinescope walls or its internal coatings.
A heavy antenna biasing can, for instance, also react upon the electron beam gun structure causing it to be deviated or misaligned from its intended position.
It is therefore an object of the present invention to provide a getter assembly free from one or more of tne disadvantages of prior getter assemblies.
Another object of the present invention is to provide an improved support means for a getter assembly which does not provoke cracking of glass walls with which it is in contact.
A further object of the present invention is to provide an improved getter assembly support means which does not cause the getter assembly to change its orientation during flashing.